how to make a bypass button ?

@klokter You don't really want to bypass samplers from a button, if a user presses it while samples are playing you will get some nasty sound. You're better using a MIDI muter script and having your button toggle that.

But you can bypass the sampler if you really want, just type "bypass" into the API search box and find the bypassing function for child synths (I can't remember what it is).